1. Field of the Invention
This invention relates to photopolymerizable compositions and, more particularly, to photopolymerizable compositions, which contain a photopolymerization initiator of a novel composition and which are sensitive, e.g., even to argon laser light.
2. Description of the Prior Art
In the past, it is well known to form an image by preparing a photopolymerizable composition comprising an unsaturated compound having at least one addition polymerizable ethylenically unsaturated double bond (hereinafter referred to as an ethylenically unsaturated compound), a photopolymerization initiator and, if required, a high molecular weight material having a film-forming ability, a thermal polymerization inhibitor, a plasticizer, and the like, preparing a solution of the photopolymerizable composition, coating the solution of the photopolymerizable composition on a support to form a light-sensitive material having thereon a layer of the photopolymerizable composition (hereinafter "light-sensitive layer"), image-wise exposing the light-sensitive layer through a desired original image, thereby causing a photopolymerization to occur in the exposed areas and harden the light-sensitive layer in the exposed areas, and then dissolving out the light-sensitive layer in the unhardened areas by treating the light-sensitive layer with an organic solvent capable of dissolving only the unhardened light-sensitive layer, thus forming an image by the hardened light-sensitive layer; or to form an image by adhering the above-described light-sensitive material to another image support (with either of the support of the light-sensitive material or the image support being transparent) to form a laminate, image-wise exposing through the transparent support, thereby causing photopolymerization to occur in the exposed areas of the light-sensitive layer, resulting in a change in the adhesive strength of the light-sensitive layer to the support of the light-sensitive material and to the image support so that the relative relationship between the adhesive strength to the support of the light-sensitive layer and the adhesive strength to the image support in the exposed areas becomes different from that in the unexposed areas, and then peeling off (delaminating) both supports from each other to separate them with the light-sensitive layer in the unexposed areas remaining adhered to one of the supports and the light-sensitive layer in the exposed areas remaining adhered to the other support, thus forming images by the light-sensitive layer on the respective supports. In the above methods, benzil, benzoin, anthraquinone or Michler's ketone have been used as photopolymerization initiators. However, although photopolymerizable compositions in which these photopolymerization initiators are used are sensitive to ultraviolet light of relatively shorter wavelengths, they are not very sensitive to ultraviolet light of longer wavelengths and visible light such as light of an argon laser and, thus, do not exhibit any polymerization-initiation ability. This becomes a problem because it is very desired as an image-forming technique to be able to use visible light or laser light which permits scanning exposure as the light for exposure in the above image-formation.